The present invention relates to heat sensitive devices and, more particularly, to a heat sensitive tape and method of making same.
Heat sensitive devices which are characterized by the use of semiconductive materials having inverse temperature-resistance characteristics in conjunction with dissimilar thermoelectric conductors are now well known in the art. Such devices are particularly suitable where it is desired to monitor the greatest temperature existing along the length of a cable, for example, and are exemplified in connection with a system for measuring and locating temperature conditions of interest in U.S. Pat. Nos. 3,408,607 and 4,324,138. Thermistor cables which are characterized by a core of semiconductive material surrounded by a mass of temperature-resistant electrically-insulating material covered with a protective metallic sheath are also well known in the art.
Despite the clear advantages and many applications for such devices, they have simply not evolved to the point of providing the desired degree of versatility. It has remained to develop a heat sensitive tape capable of generating a measurable and predictable voltage when the entire length of the tape is at ambient, e.g., 72.degree. F., wherein the tape is also adapted to provide a change in the temperature representative measurable voltage with an increase in temperature above the prevailing ambient temperature at any location along the tape. If this could be achieved with an electrical insulation having a negative temperature coefficient, the thermoelectric output of the tape or a section thereof would be altered in a predictable fashion.
Moreover, if this could be achieved, the tape location where an increase in temperature takes place could be located electronically. This could be done, for instance, as fully disclosed and claimed in my earlier U.S. Pat. No. 4,324,138, issued Apr. 13, 1982, for a method of and apparatus and system for determining temperature conditions. As set forth therein, the applications are virtually limitless.
While the value of heat sensitive devices has long been recognized, it has remained to provide a heat sensitive tape having the requisite versatility for the many applications to be benefited by use thereof. In fact, despite my many prior inventions in this field, as exemplified by U.S. Pat. Nos. 3,408,607 and 3,513,432, the missing link to providing a highly versatile heat sensitive tape, in addition to the heat sensitive cables I have previously developed, has remained. Despite the advantages that will be recognized by those skilled in the art, heat sensitive tape which may not only be utilized to monitor ambient temperature but also may be utilized to monitor for any localized increase above ambient temperature has simply not been available.
It is therefore an object of the present invention to provide a heat sensitive tape having means for generating a temperature representative measurable voltage.
It is also an object of the present invention to provide a tape of the type described utilizing an elongated flexible strip of electrically non-conductive material.
It is a further object of the present invention to provide a tape of the type described which comprises a temperature monitoring device having a pair of thermoelectric conductors disposed in spaced apart relation to extend along the strip of electrically non-conductive material in contact with means for passively self-generating a temperature representative measurable voltage between the conductors when the tape is exposed to ambient temperature.
It is another object of the present invention to provide a tape of the type described which is not only passive and self-generating to generate a voltage potential between the thermoelectric conductors indicative of the temperature existing along the entire length of the tape, i.e., the ambient temperature, but which also generates a voltage potential between the thermoelectric conductors indicative of the hottest point along the length of the tape if the temperatures are unequal.
It is still another object of the present invention to provide a tape of the type described in which the passive self-generating characteristic causes a change in the temperature representative measurable voltage with an increase or decrease in temperature at every location along the strip.
It is still another object of the present invention to provide a tape of the type described wherein the passive self-generating characteristic causes a change in the temperature representative measurable voltage with an increase in temperature above the prevailing ambient at any location along the strip.
It is still another object of the present invention to provide a tape of the type described capable of precise, non-perishable, reproducible measurement of the temperature and identification of the location of the hottest spot when monitoring with a high input impedance temperature device.
It is still another object of the present invention to provide a tape of the type described wherein the elongated flexible strip, the electrical insulation, and the thermoelectric conductors can be formed of various materials and combinations of materials to yield various mechanical properties and temperature-voltage response curves.
It is a further object of the present invention to provide a tape of the type described which can be produced in lengths of thousands of feet at a low cost to facilitate utilization in a wide variety of applications including the home.
An additional object of the present invention is to provide a tape of the type described utilizing commercially available materials and processes to manufacture the tape.
These and other objects, advantages and features of the present invention will be apparent from a consideration of the accompanying specification, claims and drawings.